1. Field of the Invention
The present invention relates to an assist control apparatus for a hybrid vehicle for which the cylinders can be stopped. In particular, the invention relates to an assist control apparatus for a hybrid vehicle that can smoothly perform a shift from the cylinder deactivating operation, which closes both intake valves and exhaust valves of an engine, to the normal operation.
2. Description of the Related Art
Heretofore there is known a hybrid vehicle incorporating a motor in addition to an engine as drive sources for vehicle propulsion. One type of such a hybrid vehicle is a parallel hybrid vehicle where the drive output from the engine is assisted by the motor.
In the parallel hybrid vehicle, at the time of acceleration the drive output from the engine is assisted by means of the motor, while at the time of deceleration, various control is carried out such as performing battery charging by deceleration regeneration, so that the residual capacity (electrical energy) of the battery can be maintained while satisfying the requirements of the driver. Furthermore, since the structural mechanism is such that the engine and the motor are arranged in series, the structure can be simplified, and the weight of the whole system can be kept low. Therefore, there is an advantage in that there is a high degree of freedom in vehicle assembly.
As the aforementioned parallel hybrid vehicle, there is a construction in which a clutch is incorporated between the engine and motor (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2000-97068) in order to avoid the influence of engine friction (engine braking) at the time of deceleration regeneration, or the engine, motor and transmission are connected in series (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2000-125405) in order to achieve maximum simplification.
However, in the former construction in which a clutch is installed between the engine and motor, there are disadvantages in that the construction is complicated by the clutch installation and the assembly becomes more difficult, and in addition the transmission efficiency of the power transmission system when running is reduced due to usage of the clutch.
On the other hand, in the latter construction in which the engine, motor and transmission are connected in series, since the amount of regeneration is reduced by the aforementioned engine friction, the electrical energy that could be conserved by regeneration is reduced. Therefore, there is a problem in that the amount of drive assist (assist amount) and the like by the motor are limited.
Furthermore, for a method of reducing engine friction during deceleration in the former type, there is a method for increasing the amount of regeneration by controlling the throttle valve opening at the time of deceleration using an electronic throttle control system to reduce pumping losses. However, since a large amount of fresh air flows as is into the exhaust system, it reduces the temperature of a catalyst and an A/F sensor, and there is a problem in that optimum exhaust gas control is affected detrimentally.
It is an object of the present invention to provide an assist control apparatus for a hybrid vehicle, which can improve the fuel consumption by the amount by which the engine friction is reduced by making the cylinder deactivating operation possible, and that can smoothly perform a shift from the cylinder deactivating operation to the normal operation.
According to a first aspect of the present invention, an assist control apparatus for a hybrid vehicle comprises an engine as a drive source of the vehicle, and a motor assisting drive of the engine in accordance with driving conditions of the vehicle, wherein the engine is a cylinder deactivating engine which can perform a normal operation and a cylinder deactivated operation, and there is provided a cylinder resumption assist judgment device which judges whether the drive of the engine should be assisted by the motor, when the engine shifts from the cylinder deactivating operation to the normal operation, and when the cylinder resumption assist judgment device detects a resumption from the cylinder deactivated condition and judges that a throttle opening is larger than a predetermined value, drive of the engine is assisted by the motor.
According to this construction, when the cylinder resumption assist judgment device judges a shift from the cylinder deactivating operation to the normal operation, and judges that the throttle opening is larger than a predetermined value, the driving force of the engine which is insufficient due to the cylinder deactivation can be assisted by the motor. As a result, there is the effect that the shift from the cylinder deactivating operation to the normal operation can be smoothly performed without an unpleasant feeling.
In a second aspect of the present invention, the hybrid vehicle comprises an automatic transmission, and the cylinder resumption assist judgment device judges whether the drive of the engine should be assisted by the motor based on the throttle opening and the vehicle speed.
With such a construction, the acceleration intention of the driver can be grasped from the throttle opening and the vehicle speed, instead of the inlet pipe negative pressure, which cannot be used as a reference for judgment, since the cylinders are in the deactivated condition. As a result, there is the effect that the driver""s intention can be accurately realized in a hybrid vehicle having an automatic transmission.
In a third aspect of the present invention, the hybrid vehicle comprises a manual transmission, and the cylinder resumption assist judgment device judges whether the drive of the engine should be assisted based on the throttle opening and the engine speed.
With such a construction, the acceleration intention of the driver can be grasped from the throttle opening and the engine speed, instead of from the inlet pipe negative pressure, which cannot be used as a reference for judgment, since the cylinders are in the deactivated condition. As a result, there is the effect that the driver""s intention can be accurately realized in a hybrid vehicle having a manual transmission.
In a fourth aspect of the present invention, an amount of drive assist by means of the motor is determined base on engine speed and throttle opening.
With such a construction, since a setting is possible where an engine output equal to the engine output used in the normal operation can be generated, there is the effect that a similar feeling to the acceleration feeling at the time of normal operation can be provided, and the operation can be shifted to the normal operation without an unpleasant feeling.
In a fifth aspect of the present invention, drive assist by means of the motor is continued for a predetermined period of time, after the engine has resumed from the cylinder deactivated operation and the fuel injection amount has been gradually increased and has reached a predetermined value.
With such a construction, the drive of the engine can be assisted by the motor, until the engine generates the normal output, after having resumed from the cylinder deactivated condition and the fuel injection amount has reached a predetermined amount.